Vacuum cleaner anecdote. We had to clean a bunch of very narrow crevices, so I suggested attaching a straw with tape to the end of the normal crevice tool. It worked. But after a few minutes, vacuum overheated and shut down. Took 25 minute cool-down before it reset itself.
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I was kinda mad at myself because it's sort of mechanical engineering 101 that you don't run a compressor outside its rated pressure difference, but glad the design was good. Anyhow, started wondering how the overheating actually happens...
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Hypothesis 1: motor draws too much current to work against the too-high pressure gradient and that heats the winding too much?
Hypothesis 2: the higher pressure puts more mechanical stress on the shaft/bearing coupling, causing more frictional heating there?
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I'm guessing it's hypothesis 1. The motor probably has a speed regulator which tries to drive up current to keep the speed constant.
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Also, this made me realize I don't quite understand what happens when a motor is put in stall. I'm guessing because the inductive coupling is no longer doing rotational work on the shaft, but the current is constant or rising, it has to get translated into heat somehow?
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Everything has way too much detail to understand. Just googled and learned that vacuums typically use a type of "universal motor" that's a brushed dc motor designed to run off AC. I think we had a week of lectures on motors in EE 101 and I've forgotten even that.
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1/2 Hyphothesis 3 - sucked-in air on the way out from the vacuum bag is cooling the motor and you restricted the air flow, hence there was nothing to receive the heat from the motor.
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2/2 same thing happens when running angle grinders and drill on slow speed as the motor is designed to generate the cooling airflow by itself
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